Environmental Engineering Reference
In-Depth Information
10 kilowatts. All other solar thermal power plants should have a minimum output
of 10 megawatts. Effi ciency is increased even further if output levels are between
50 and 200 megawatts. Optimally, a system should be one square kilometre or more
in total size to make it economically viable.
The main advantage of solar thermal systems is the simple integration of thermal
storage. Small storage units used for a few hours only minimally increase the cost
of generating electricity at solar thermal plants. However, they ensure that the power
output of the plants can be guaranteed and, as a result, increase the availability and
the value of electric energy.
7.5 Ecology
Solar power plants without fossil fuel backup facilities do not release any direct
carbon dioxide emissions during operation. When a fossil fuel-fi red parallel burner
exists, as is the case with some solar thermal parabolic trough power plants, the
natural gas portion should be kept to an absolute minimum. Due to the low tem-
peratures, the effi ciency of solar thermal plants for electricity generation is lower
than that of optimized pure natural gas plants. This aspect is insignifi cant when
power plants are run purely on solar power. However, if fossil fuels are burnt as
well, the carbon dioxide emissions rise. It is accepted that the addition of fossil fuel
will increase supply reliability and protect against frost. But the fossil portion should
not exceed 10% to ensure effective environmental protection.
Some World Bank projects in developing countries are striving towards an integra-
tion of relatively small parabolic trough collector fi elds into conventional gas and
steam power plants run on natural gas. Due to technical restrictions, the solar portion
is clearly below 10% there. This type of ISCCS (Integrated Solar Combined-Cycle
System) is not suitable for effective climate protection.
Compared to conventional photovoltaic systems, the production energy required for
thermal solar power plants is lower. Within a year a solar power plant will deliver
more energy than was originally used to produce the plant.
Unlike small photovoltaic and solar thermal systems, solar systems cannot be inte-
grated into buildings. Instead they need large open areas of space comprising many
hectares. Ideally, solar plants should be erected in thinly populated areas where the
land is not needed for other purposes. Fortunately, many sunny regions on earth
have these very characteristics. Very little grows in hot deserts where the sun shines
almost all year round, and the human populations tend to be low. Solar thermal
power plants built on suitable desert sites would easily be able to meet the electricity
demands of the entire planet a hundred times over.
The main problem with thermal systems is the need for cooling water. Water is
often a scarce resource in sunny regions. The small number of power plants installed
until now have always been able to fi nd local water reserves for the cooling. On a
larger scale freshwater cooling in regions with little water is a problem. In principle,
a solar thermal power plant can also operate with dry cooling. In this case, effi ciency
